This invention relates to leaching metals from metal-containing particles, such as laterite or spent hydroprocessing catalysts.
One modern development in crude oil processing is the upgrading of metal-containing and sulfur-containing feedstocks such as crude oils and residua by hydroprocessing methods. Such upgrading is necessary to convert the heavy feedstock into more valuable, lower boiling fractions, and to remove metals and sulfur contaminants. These contaminants can pollute the atmosphere upon combustion.
Crude oils contain various dissolved contaminants, such as nickel, vanadium, iron and sulfur. The lighter fractions are frequently distilled off under either atmospheric pressure or a partial vacuum, leaving the metals in a high boiling fraction called the "residua". The residua will generally contain at least about 35 ppm metal contaminants and frequently as high as 100 ppm. In extreme cases, the residua can contain more than 1000 ppm metal contaminants.
The contaminant metals, and any sulfur which is present, are removed by processing the feedstock with a catalyst in the presence of hydrogen. Such catalysts are generally a solid support that contains catalytic metals, generally a Group VIII metal alone or in conjunction with a Group VI metal. The Group VI metal is typically tungsten or molybdenum and the Group VIII metal is typically nickel or cobalt. As the catalyst is used, metals from the feedstock deposit on its exterior surface and the interior surface of its pores, eventually plugging the pores and reducing the activity of the catalyst to such a degree that it does not give the desired product quality. Such catalysts are herein defined as "spent catalyst," and contain catalytic metals, an inorganic support matrix, metals removed from the feedstock sulfur compounds, and a hydrocarbonaceous residuum.
Recently, the crude oil which has been obtained tends to be heavier, forcing refiners to use more hydroprocessing catalysts than previously necessary to remove metals and sulfur from the feedstock. It is expected, therefore, that a shortage will develop of the valuable catalytic metals, particularly cobalt. As a result, efforts have been made to extract metals from hydroprocessing catalysts so that the catalytic metals, the deposited metals, and the catalyst supports can be reused.
One process of leaching hydroprocessing catalysts is described in U.S. Pat. No. 3,567,433. In that process an aqueous ammonia and ammonium salt leach solution is contacted with spent catalyst particles.
Another leaching process is described in Chemical Abstracts, 94:178649x. In that process, a spent catalyst containing aluminum, vanadium, nickel, cobalt and molybdenum is leached with ammonia and ammonium salts, at a temperature greater than 110.degree. C. and an oxygen partial pressure of greater than 1 kg/cm.sup.2, for more than 1/2 hour. Such conditions require autoclave reactors.
U.S. Pat. No. 4,216,118 describes chlorinating spent catalysts to convert vanadium values to vanadium tetrachloride and nickel values to nickel chloride for recovery by solvent extraction.
U.S. Pat. No. 4,145,397 describes the recovery of metals from spent catalysts by roasting at high temperatures and leaching with caustic alkali.
U.S. Pat. No. 4,432,949 describes separating metal values from an aqueous stream containing vanadium, molybdenum, nickel and cobalt. In that process, vanadium is first precipitated, and then nickel, cobalt, and molybdenum are removed by serial ion exchange.
U.S. Pat. No. 4,434,141 describes recovering metal values from an aqueous stream. The metal values are preferably obtained by leaching spent hydroprocessing catalysts which include nickel, cobalt, vanadium and molybdenum. The metal values are extracted, isolated and purified by liquid, liquid extraction techniques.
An article in Engineering and Mining Journal (May 1978, page 105), describes a plant designed to process spent catalyst containing no cobalt by first leaching with sodium hydroxide and then with ammonium carbonate.